Legal advice about my job....please help?

so ive been working at a nursing home since august of 2010 thats 8 months and ive been working around 30 to 40 hours a week...i went out for maternity leave and they hired 2 ppl in my department to take my place while i was out...i had my son april 6 2011 i went back to work 6 weeks later and ive had 2 days of work i worked one day last month (june) and one day this month (july) i am scheduled to work sunday night and monday night...so basically the 2 ppl they hired while i was out have my hours now...they cant do this can they? is this illegal and what can i do about it?